1. Field of the Invention
The present invention relates to a CT image processing device and a CT image processing method in which a portion of a subject is scanned by an X-ray CT device in synchronization with a periodic motion thereof and obtained projection data is processed so as to reconstruct an image.
2. Description of the Related Art
X-ray CT scanning is effective for in vivo observation of an animal such as a mouse and a rat. However, animals cannot stop breathing during CT scanning in accordance with an instruction of an operator as humans do. Moreover, hearts cannot stop during biological scanning. Therefore, images of hearts, lungs and neighboring organs such as livers are blurred by influences of heartbeat and breathing, and the X-ray CT is not suitable for observation or inspection of fine portions.
An X-ray CT device capable of breathing beat synchronized scanning has been developed because of the above-described circumstances. In devices of Japanese Unexamined Patent Application Publication No. 2008-228828 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2008-228829 (Patent Document 2), for example, a region of interest is set so as to include a region of a periodic motion portion of a subject, and a characteristic amount obtained by integration over the region of interest is calculated as a synchronization signal of the periodic motion of the subject. Then, rotation of a gantry is controlled by shifting a phase using the synchronization signal of the periodic motion, to perform X-ray CT scanning, and interpolation processing is performed with data scanned in a plurality of rotations.
Moreover, in a controller described in Dinkel et al, Intrinsic Gating for Small-Animal Computed Tomography A Robust ECG-Less Paradigm for Deriving Cardiac Phase Information and Functional Imaging, Journal OF THE American Heart Association, USA, American Heart Association, Circ Cardiovasc Imagin 2008; 1; 235-243 (Non-patent Document 1), breathing beat is obtained by placing a pressure sensor in the vicinity of a subject chest portion, while electrodes are punctured on the both shoulders and a foot portion of a subject, and ECG measurement is made so as to obtain a heartbeat signal. Then, several sessions of CT scanning are performed while a phase is shifted with respect to the breathing beat, CT angle data with the same phase is selected and organized into single CT data, and image reconstruction of the synchronous CT data is executed.
On the other hand, some X-ray CT scanning devices calculate a position of a region in accordance with a scanning angle on the basis of the region set in a scanned image. In an X-ray blood vessel imaging device described in Japanese Unexamined Patent Application Publication No. 2006-346263 (Patent Document 3), a gate area is stored with respect to an inspection portion and a scanning angle, and the stored gate area corresponding to the inspection portion and the scanning angle is set for each scanned image. At that time, gate area information is created for the set scanning angle from the gate area information registered for the angles nearby.